@RickiTarr
While there are lots of reasons for this, one is a particular piece of research.

Aboriginal Australians generally eat what the poor in many Western countries eat: mostly carbs and sugar and precious little vegetables. The study has them switch to a diet more like what their distant ancestors ate, and there were tons of health improvements.

But those improvements came from what they stopped eating, not what they started eating. A lot of people drew the wrong conclusions.